1. Field of the Invention
This invention relates to a transmitting method and apparatus, a sending power controlling method, and more particularly, suitably applied to a cellular radio communication system.
2. Description of the Related Art
In a cellular radio communication system, areas for offering communication service are divided into cells that have the desired size; a transmitting apparatus is placed in each cell as a fixed station. A communication terminal unit, that is a mobile station, will communicate with such a transmitting apparatus that is in the best status to communicate.
By the way, such a cellular radio communication system, when the desired communication is to be performed, may have the case where the transmission must be performed with a large sending power and the case where the lower sending power is enough to communicate, depending on the position of the mobile station. Therefore, in the cellular radio communication system, a transmitting apparatus and a communication terminal unit are monitoring a received power of each other, and they mutually notify power controlling information based on the result of the monitoring, so as to form a feedback loop and to perform sending-power controlling wherein the communication is achieved with the minimum sending power that is needed. Thus, the cellular radio communication system makes it possible to communicate efficiently with the minimum sending power and to reduce the consumption power in comparison with the case of fixed-power communication, so that such an effect can be obtained that the life time of the battery of a communication terminal unit can be elongated.
In such the cellular radio communication system, it is able to suppress excess sending power by performing transmission on the basis of the power controlling information that is informed from the partner of the communication, however, it is not able to maintain communication continuously by merely controlling the sending power on the basis of the power controlling information.
For instance, it is supposed that a transmitting apparatus 1 is communicating with communication terminal units 2A to 2D existing within the base station's own cell, wherein the transmitting apparatus 1 is communicating with the communication terminal unit 2A using a down channel f1, communicating with the communication terminal unit 2B using a down channel f2, communicating with the communication terminal unit 2C using a down channel f3, and communicating with the communication terminal unit 2D using a down channel f5, as shown in FIG. 1. Besides, it is assumed that the communication terminal units 2A, 2C and 2D are relatively distant from the transmitting apparatus 1, and the communication terminal unit 2B is relatively near to the transmitting apparatus 1.
If sending power controlling is performed under such a situation, the transmitting apparatus 1 transmits transmission signals having relatively large sending power to the communication terminal units 2A, 2C and 2D, and transmits a transmission signal having relatively small sending power to the communication terminal unit 2B. This is because the signal power that are received by the communication terminal units 2A, 2C and 2D are diminished relatively, since signal loss on the transmission line is in proportion to the distance. Therefore, under such a situation, the communication terminal units 2A, 2C and 2D notify the power controlling information of increasing the sending power to the transmitting apparatus 1; as a result, the transmitting apparatus 1 performs transmission to the communication terminal units 2A, 2C and 2D, with a relatively large sending power.
FIG. 2 shows the situation of the sending power of this instance. As shown in the FIG. 2, the transmitting apparatus 1 transmits the transmission signals S1, S3 and S5 of the down channels f1, f3 and f5 that are used for communication with the communication terminal units 2A, 2C and 2D with the large sending power, and transmits the transmission signal S2 of the down channel f2 that is used for communication with the communication terminal unit 2B with the small sending power.
By the way, when a transmission signal is transmitted from a transmitting apparatus 1, usually, the transmission signal is filtered to limit its band width, so that the signal is not transmitted to other channels than the allocated channel. For instance, the band of the transmission signal S1, which is transmitted through the down channel f1, is limited such that it falls within the band of the channel f1. However, it is not possible to completely limit the band by the filter in practice, and some signal components that leak into the adjacent channels exist. This leakage of signal components into adjacent channels is an unavoidable problem, because it is difficult to manufacture a filter that is able to completely cut off such out-of-band signal components.
In fact, in the situation shown in FIG. 2, the transmission signal S1 that is transmitted through the down channel f1 is leaking, in part, into the adjacent channels f0 and f2, and the transmission signal S3 that is transmitted through the down channel f3 is also leaking, in part, into the adjacent channels f2 and f4. If the adjacent channels are not being used or the electric power of the transmission signals that are transmitted through the adjacent channels are large, the signal components that leak into the adjacent channels offer no problem; however, if the power of the transmission signals that are transmitted through the adjacent channels are small, the leaked signal components come into question, because the leaked signal components work as interference waves.
The good example is the channel f2 shown in FIG. 2. When the sending power of a transmission signal S2 is small as the channel f2, the transmission signal S2 is buried in the signal components that have been leaked from the adjacent channels f1 and f3; as a result, although the transmission is being performed with the sending power that has been required from the reception side, the signal-to-interference power ratio C/I deteriorates, and it becomes difficult to perform communication satisfactorily.
In this way, even if transmission is performed with the sending power required from the partner of the communication, it is sometimes difficult to maintain the communication satisfactorily because of the influences of the adjacent-channel interference; thus, the conventional transmission power controlling is yet unsatisfactory.